The present invention generally relates to sporting equipment and, more particularly, to a portable swing speed analyzer that is specifically adapted to be releasably mounted on a hand-held sporting implement such as a golf club. The swing speed analyzer is configured to measure swing parameters such as velocity during impact with an object such as a golf ball and to display the swing parameters on a display device. The swing speed analyzer may be further configured to measure bending in the hand-held sporting implements such as a golf club shaft, during a forward swing in order to determine whether potential energy resulting from bending of a golf club shaft is released at the instant when the golf club strikes the golf ball.
Many sporting activities such as golf, tennis and baseball utilize a swinging implement such as a golf club, a tennis racket, or a baseball bat to strike an object, such as a golf ball, a tennis ball or a baseball. In such activities, it is often desirable to maximize the swinging speed of the swinging implement. Furthermore, it is desirable that the maximized speed of the swinging implement occurs when the swinging implement impacts the object. For the case in which the swinging implement is a golf club, it is desirable that the maximized speed occurs at the instant when the golf club impacts the golf ball.
The prior art includes numerous devices for measuring the swinging speed of swinging implements such as those used in the above-mentioned sporting activities. Such devices may be generally referred to as swing speed analyzers. Prior art swing speed analyzers that are configured to measure the swinging speed of a golf club may be generally classified as one of three types. The first type of swing speed analyzer is comprised of an instrumented mat having embedded sensors. The embedded sensors measure and record the velocity of the club head as well as the angular orientation and direction of travel of a face of the club head during its impact with the golf ball. The second type of swing speed analyzer utilizes a radar device or a radar gun that is placed adjacent to the golf ball. The radar device measures and records the maximum velocity of the club head.
The third type of swing speed analyzer utilizes an instrument that is attached to the shaft of the golf club. The instrument measures the maximum centrifugal acceleration of the golf club and, by calibration, records the maximum speed of the club head. The drawback of the third type of swing speed analyzer is that the accelerometer is not isolated from the very high shock forces when the ball is struck. As a result, the third type of swing speed analyzer is incapable of measuring the maximum speed of the club head when a golf ball is being impacted. Furthermore, this third type of swing speed analyzer is incapable of allowing the user to determine whether the maximum speed of the golf club occurred at impact with the golf ball, as is desired, or whether the maximum speed of the golf club occurred at a less critical point of the swing.
U.S. Pat. No. 4,991,850 issued to Wilhlem (the Wilhlem reference) discloses a swing speed analyzer comprised of accelerometers that are embedded within a wooden head of a golf club. In an alternative embodiment, the accelerometers may be attached to an aft face of a metallic club head of a driver type golf club. In either configuration, the swing speed analyzer of the Wilhlem reference provides a system for measuring the speed of the club head. However, the swing speed analyzer of the Wilhlem reference is not portable due to the inclusion of accelerometers that are embedded within the club head. Furthermore, the swing speed analyzer of the Wilhlem reference fails to isolate the relatively delicate and sensitive accelerometers from very high shock forces on the order of 1000's of g's that occur when the golf club impacts the golf ball.
U.S. Pat. No. 5,688,183 issued to Sabatino (the Sabatino reference) discloses a portable swing speed analyzer comprised of an accelerometer that is attached to a golfer's glove covering the user's hand. The swing speed analyzer of the Sabatino reference is configured to be portable. However, the device suffers from the drawback of having reduced accuracy in measuring the velocity of the club head due to the relatively large spacing between the accelerometer and the club head. The speed of a swinging implement may be characterized by its velocity which may be mathematically expressed by the formula, v=(a×r)0.5, where a is the centrifugal acceleration, v is the tangential velocity, and r is the radius of rotation of the accelerometer. Therefore, by locating the accelerometer adjacent the grip portion of the shaft instead of near the club head, the accuracy of the club head velocity as measured by the accelerometer is reduced by a factor of four. In addition, because the shaft of the golf club typically flexes or bends during the swing, the additional velocity of the club head that occurs due to the release of potential energy when the golf club shaft reflexes from its flexed position cannot be measured by the glove-mounted accelerometer of the Sabatino reference.
U.S. Pat. No. 5,441,256 issued to Hachman (the Hachman reference) describes an accelerometer that is attached to the head of a golf club. As understood, the Hachman reference describes a method of using the accelerometer in order to determine the bending frequency of a shaft of the golf club. A golfer swings the golf club with the accelerometer attached thereto. The same golf club is then placed in a bench-measuring device wherein the golf club is held stationery and the shaft is flexed so that the shaft bending frequency may be measured. The golfer-swung shaft bending frequency is then compared to the bench-measured shaft bending frequency. Ostensibly, the golfer uses the comparison data in order to match the flex of the shaft to the particular golfer's swing. More specifically, the above-described procedure is understood to allow a golfer to perform test swings on a number of different golf club having shafts with varying bending characteristics. Theoretically, the golfer may select a shaft having bending characteristics that match the particular golfer's swing. Once selected, a set of shafts having the desired bending characteristics may be assembled into a customized set of golf clubs that allows the particular golfer to maximize the angular acceleration of each club head of the set during regular play.
However, the Hachman reference suffers from several deficiencies that detract from its overall utility for the following reasons. During the swing of a golf club, a portion of the angular acceleration of the club head results from the rotation of the golf club by the golfer. Another portion of the angular acceleration results from the flex of the golf club shaft during the swing. Unfortunately, during the swing of a golf club, the angular acceleration of the club head due to shaft bending cannot be determined because it is overwhelmed by very high centrifugal and tangential accelerations of the club head. Based upon the above, FIG. 1 of the Hachman reference, which is described as being a graph of the angular acceleration of the club head when swung by the golfer, is believed to be inaccurate because it does not account for that portion of the angular acceleration resulting from rotation of the golf club by the golfer. Furthermore, it should be noted that no mention is made in the Hachman reference regarding using the accelerometer to determine the velocity of the club head.
U.S. Pat. No. 6,441,745 issued to Gates (the Gates reference) describes an acceleration monitor assembly having a circuit board that is releasably mounted on a golf club shaft adjacent to the club head. The circuit board includes a linear accelerometer. The axis of the linear accelerometer is aligned with the axis of the shaft such that the linear accelerometer may measure centrifugal acceleration acting on the golf club during a swing. A wireless transmitter mounted on the circuit board transmits a signal from the linear accelerometer to a remote wireless receiver that may be included in a wrist-mounted device worn by the golfer. The wrist-mounted device displays a velocity reading after the swing. As was mentioned above in the description of the Sabatino reference, the instantaneous velocity of a club head can be calculated from the output of a linear accelerometer using the previously mentioned formula v=(a×r)0.5.
However, as is pointed out in the description of the Gates reference, the radius of rotation of the club head keeps changing during the swing because of rotation of a golfer's shoulders and because of cocking and uncocking of the golfer's elbows and wrists during a swing. As a result, the acceleration monitor assembly of the Gates reference requires the use of an accelerometer calibrator for accommodating changes in the radius of rotation of the linear accelerometer. In this regard, a chronograph such as a radar gun must be utilized to first measure the actual speed of the club head. The actual speed is measured when the club head is at the bottom of the down stroke, which is approximately the position of the club head during the swing when the ball is struck. After the actual speed of the club head is measured, the circuit board and the linear accelerometer are calibrated by the accelerometer calibrator using the actual velocity of the club head as measured by the chronograph. After calibration, the output of the linear accelerometer of the Gates reference will correspond to the actual velocity of the club head. However, it should be noted that the Gates reference does not claim nor does it disclose the measurement of the club head velocity. The Gates reference only discloses the receiving of a signal generated by the centrifugal acceleration.
In the Gates reference, the acceleration that is then displayed by the wrist-mounted device is the maximum acceleration measured by the linear accelerometer that is aligned with the shaft. However, the accelerometer will typically experience shock forces of 1000's of g's when the golf ball is struck. By comparison, acceleration of the club head before the ball is struck or during a practice swing is on the order of only about 100 g's in the centrifugal direction. Thus, the maximum acceleration that is measured in the Gates reference is due to the shock on the club head when it strikes the golf ball, rather than the (desired) acceleration of the club head at the instant prior to impact. Thus, as understood, the acceleration monitor assembly of the Gates reference is incapable of determining the velocity of the club head by using a linear accelerometer for measuring centrifugal force.
Furthermore, a second embodiment of the acceleration monitor assembly of the Gates reference uses a second linear accelerometer having an axis that must be oriented perpendicular to the path of movement of the club head and also perpendicular to the shaft axis. The second embodiment ostensibly allows the golfer to determine if the golf club is moving in a direction that is transverse to the golf ball (i.e., out of the plane of swing) at the time of impact, as is undesirable. Unfortunately, any misalignment of the second linear accelerometer causes it to measure a component of the acceleration in the tangential direction. Typically, the magnitude of accelerations of the club head at the instant prior to impact with the golf ball is about 100 g's in the centrifugal direction (i.e., aligned with the shaft), is less than 1 g in the angular direction (i.e., aligned parallel to the striking surface), and about 10 g's in the tangential direction (i.e., aligned in the direction of swing at impact). Thus, even a slight misalignment of the second linear accelerometer would cause it to measure a portion of the much greater tangential acceleration.
For example, if the circuit board and, hence, the second accelerometer were clipped onto the shaft with rotation or twisting of only 5 degrees out of the plane of swing, the second linear accelerometer would measure almost 1 g. Thus, unless the acceleration monitor assembly of the Gates reference were perfectly aligned on the shaft, resultant measurements of the second linear accelerometer would not be usable in determining whether or not the golf club is moving transverse to the golf ball at the time of impact. Furthermore, even if the acceleration monitor assembly were perfectly aligned on the shaft, it would not be possible to distinguish between twisting of the club face by the golfer or out-of-plane movement of the golf club using the second linear accelerometer as a cause of inaccurate directional movement of the golf ball (i.e., hooking or slicing).
Finally, the acceleration monitor assembly of the Gates reference suffers from another deficiency in that the circuit board is mounted on the shaft with a clip. Unfortunately, as mentioned above, the 1000's of g's that are transmitted to the accelerometer when the golf ball is struck could cause the clip to fracture and/or to fall off the golf club. In addition, low-cost linear accelerometers are incapable of withstanding such extreme shock and would therefore likely fail upon first impact of the club head with the golf ball.
Even if the acceleration monitor assembly used specially manufactured or scientific linear accelerometers that were capable of withstanding 1000's of g's of shock, such accelerometers would also need a much greater sensitivity than the typical 1 percent sensitivity such that they could provide useful measurements closer to the 10 g tangential acceleration of the club head. To emphasize this point, if the acceleration at impact were only 1000 g's, 1 percent thereof is 10 g's which is equal to the tangential acceleration of the club head. Thus, a standard accelerometer that could survive the shock at impact would unfortunately be incapable of measuring the change in accelerations that occur during a typical golf swing.
As can be seen, there exists a need in the art for a swing speed analyzer that can accurately measure the swinging speed of a swinging implement, including the velocity of the swinging implement, such as a golf club, at the instant prior to impact with an object such as a golf ball. Additionally, there exists a need in the art for a swing speed analyzer that can measure the swinging speed of a swinging implement at any point during the swing. Also, there exists a need in the art for a swing speed analyzer that is portable such that the swing speed analyzer may be interchangeably mounted on a variety of alternative swinging implements such as a variety of different golf clubs that are typically used by a golfer in playing a round of golf.
There also exists a need for a swing speed analyzer that uses commonly available, low-cost battery-powered accelerometers such that the overall complexity and cost of the swing speed analyzer may be reduced. Finally, there exists a need in the art for a swing speed analyzer that isolates the low-cost accelerometer from the shock forces produced when the ball is struck.